Within the cellulose technology, apparatuses of the above-mentioned description are frequently found, where the material intended for refining is supplied through an opening in the stationary disc and is refined between the set of stationary and the set of rotary refiner elements.
Here, the amount and intensity of the refining work may be said to be controlled by the rotational speed and diameter of the rotary disc, as well as the predetermined distance between the sets of refiner elements, the so-called disc gap. Since a standard-sized refining apparatus of today may have a disc diameter of about 1700 mm, and can generate about 15 MW, a resulting refining force, i.e., the axial tie force needed to sustain a given disc gap, corresponding to 80 kN or more, may be required.
The size of the disc gap, dependent on the process, starting material and desired fiber quality, may vary between about 0.2 and 1.0 mm. Irrespective of the nominal size of the disc gap, it is, however, of utmost importance in terms of or the refining result that the size of the disc gap be is constant, in spite of fast variations in the flow of refining material.
In recent years, the trend within this field of cellulose technology has been toward finer paper qualities, which means more refining work, which in turn has required larger disc diameters, greater rotational speeds, and above all smaller disc gaps. This has thus elucidated another important area, the parallelism between the sets of refiner elements, i.e. the deviation of the disc gap around the periphery of the disc.
Previously, a deviation of about 0.05 mm has frequently been accepted as a rule of thumb, but with a decreasing nominal disc gap, down to about 0.2 to 0.3 mm, and this has become increasingly difficult to accept. Furthermore, the larger diameters have made it more difficult to adjust the machine to such precision. This adjustment has, moreover, to be carried out with the machine not running in a cool state. The thermal expansion which occurs during operation naturally involves additional deviations, since the trend is also toward higher process pressures, and thus higher temperatures. Simultaneously, greater demands have also been made on the stiffness of the machine, i.e., the size of the disc gap must not vary too much with the refining force.
One of the objects of the present invention is to provide a refining apparatus which has the set of refiner elements of the stationary disc self-adjusting parallelism-wise in relation to the set of refiner elements of the rotatable disc, without the axial stiffness of the machine being appreciably impaired.